1. Field of the Invention
The present invention relates to an electron beam sterilizer for irradiating an article that is being fed by a feeder with an electron beam to sterilize the article, and more particularly to an arrangement for carrying out maintenance work on an electron beam irradiation unit for radiating an electron beam.
2. Description of the Related Art
Electron beam sterilizers generally include an article feeder for successively feeding articles into an isolated sterilization chamber and an electron beam irradiation unit having an irradiation window positioned in facing relation to an opening in the sterilization chamber, thereby coupling the sterilization chamber and the electron beam irradiation unit to each other. Articles that are fed into sterilization chamber by the article feeder are sterilized by an electron beam that is applied from the electron beam irradiation unit through the irradiation window to the articles.
The irradiation window of the electron beam irradiation unit is fitted with a metal foil of titanium or the like. Periodic maintenance work needs to be performed on the irradiation window for replacing the metal foil with a new metal foil, etc. The maintenance work involves not only replacing the metal foil with a new metal foil but also evacuating a chamber of the electron beam irradiation unit after the metal foil has been replaced and actually applying the electron beam to the new metal foil for adjustments.
When the electron beam is applied to the new metal foil for adjustments, the irradiation window of the electron beam irradiation unit is positioned in facing relation to the opening in the sterilization chamber in order to prevent X-rays from leaking out. If the electron beam is applied while the article feeder is not in operation, then the electron beam remains continuously applied to a localized area of the article feeder, tending to overheat and thermally deform the localized area. To avoid such a difficulty, the electron beam is applied while the article feeder is in operation. The process of applying the electron beam to the new metal foil for adjustments after it has replaced the old metal foil usually takes six to seven hours. Therefore, other tasks such as maintenance work on the article feeder cannot be performed during the process, making the electron beam sterilizer inefficient in its operation.
There has already been proposed a technology for preventing articles from being lowered in quality by the application of an electron beam during a maintenance process (see, for example, Japanese laid-open patent publication No. 9-15399). According to the invention disclosed in the above publication, a removable electron beam shield is disposed between an irradiation window and an article which is irradiated with an electron beam to prevent the electron beam from directly reaching the article during the maintenance process. The publication also discloses that the electron beam shield includes a cooling mechanism for dissipating the heat generated when the electron beam shield is irradiated with the electron beam.
According to the invention disclosed in the publication, the electron beam shield is positioned in the processing zone of a feed path along which the article travels. Consequently, the electron beam shield needs to be removed after the maintenance work. However, since ozone that is produced by the applied electron beam leaks out when the electron beam shield is removed, the working environment tends to be adversely affected by the ozone leakage. In addition, it is not easy to install the electron beam shield in the processing zone of the feed path and remove the electron beam shield from the processing zone of the feed path. Furthermore, it is not possible to carry out maintenance work on the article feeder while maintenance work is being performed on the electron beam irradiation unit.